By the time Michael advanced to the 1st Tier, he had already used Extraction to aid his first natural cleansing.
Extracting impurities from his body wasn't possible under ordinary circumstances. It seemed like he could only meet the conditions to extract impurities during a natural cleansing.
That was also why Michael used 6-Star Extraction, strengthened by several layers of Enhancement during his second natural cleansing.
The fewer impurities he left inside his body the faster his energy circulation would be. At the end of the day, the overall strengthening he received from his War Rune's advancement would be on the higher side with fewer impurities restricting him.
A body void of impurities was what Michael worked toward. Perfectly purifying himself would increase his strength drastically, and using 6-Star Extraction was his approach to get closer to his final goal.
